1. Technical Field
The present invention relates to a flow control device for supplying a specified mass flow volume of a gas or the like for a semiconductor manufacturing process or the like, and particularly to the improvement of the responsiveness of a flow control device.
2. Related Art
Typically, a flow control device is used for supplying a specified mass flow volume of gas or the like for a semiconductor manufacturing process or the like. With this kind of flow control device, a flow volume sensor and control valve are provided in the flow path in which the gas or the like flows. Then, the detection value of the flow volume sensor is compared with a flow volume setting signal, and the valve opening degree of the control valve is controlled based on the difference between these two. With the semiconductor manufacturing process, the responsiveness of the flow control device has a significant effect on semiconductor manufacturing productivity. Various improvements of the responsiveness of the flow control device have been made in the past for flow control devices.
For example, with the flow control of the technology in Unexamined Patent Publication No. 2001-147723, when the flow volume set value is changed, an initial voltage that is slightly smaller than the control valve drive voltage found from the deviation between the flow volume setting signal and the flow volume sensor detection value is applied to the control valve, and immediately thereafter, this shifts to velocity type PID control. Then, with this method, it is possible to set to a desired flow volume quickly without the overshoot.
Also, the mass flow controller of Unexamined Patent Publication No. 2002-41149 is provided in the flow path in which the fluid flows, a flow volume sensor provided in the flow path, and a PID circuit that outputs control signals for controlling the control valve so that the measured value according to the flow volume sensor is the set value according to the flow volume setting signal. The mass flow controller is provided with a response improvement circuit that outputs a correction signal to the PID circuit during the time from when the flow volume setting signal is input until the flow volume sensor detects the flow of the fluid. The mass flow controller with such features improves the responsiveness of the flow control device.
Furthermore, the valve control device of Unexamined Patent Publication No. H09-171412 has: a first calculation means for calculating the optimal valve opening degree from the set flow volume and the feed forward calculation formula; a comparison means for comparing the actual flow volume detected by the flow volume detection means and the set flow volume and finding the deviation between them; a second calculation means for performing PID control calculation based on the deviation obtained by the comparison means; and a third calculation means for adding the calculation results of the first calculation means and the calculation results of the second calculation means. Also, the control responsiveness becomes faster by obtaining the optimal valve opening degree using the feed forward calculation formula, and it is possible to add fine tuning by finding a correction volume for the optimal valve opening degree using the PID control calculation.
With the technology noted in Unexamined Patent Publication No. 2001-147723, the responsiveness of the flow control when the flow volume set value is changed is improved. However, since the PID control remains dominant. Accordingly, the increase in the response speed is insufficient.
With the technology noted in Unexamined Patent Publication No. 2002-41149, by providing a response improvement circuit that outputs correction signals to the PID circuit, flow control is improved. However, a huge number of manhours is required to adjust the size of the correction signal and the threshold value that regulates the length of time that the correction signal is output. This is because since the correction signal controls the control valve via the PID circuit, if the PID gain changes, the correction signal size or threshold value must be readjusted.
With the technology noted in Unexamined Patent Publication No. H09-171412, the feed forward calculation output results are always applied even during control. Accordingly, when adjusting the feed forward parameter and feedback parameter to realize optimal control responsiveness, the correlation between both parameters has to be considered and adjusted. Specifically, when either the feed forward parameter or the feedback parameter is changed, this has an effect on the other parameter. Accordingly, there was the problem that it takes time to adjust the feed forward parameter and the feedback parameter.
The improvements in responsiveness and the problem of balancing feedback control and feed forward control described above are not limited to flow control with a mass flow meter used with the semiconductor manufacturing process, but exist with various fluid flow controls.